Referring to FIG. 1, there is shown a conventional power filtering design wherein a multilayer circuit board 10 has a power plane 12 and a ground plane 14 for providing power and around to an integrated circuit component 16 mounted on the multilayer circuit board 10. That is, the integrated circuit component 16 has a plurality of leads 18, including a power lead 18a, a around lead 18b, and a plurality of signals leads 18c. The integrated circuit component 16 is mounted on the multilayer circuit board 10 such, that the power lead 18a is electrically connected to the power plane 12, the ground lead 18b is electrically connected to the ground plane 14, and the signal leads 18c are electrically connected to signal conductors (not shown) formed on other layers of the multilayer circuit board 10. Thus, the power plane 12 provides power to the integrated circuit component 16, while the ground plane 14 provides a ground for the integrated circuit component 16.
When the integrated circuit component 16 is operating at high frequencies, high frequency noise often results on the power and ground planes 12 and 14 due to high speed internal switching within the integrated circuit component 16, resulting unsteady current requirements. To alleviate this high frequency noise problem, bypass capacitors are often electrically connected between power planes and ground planes on multilayer circuit boards. For example, in FIG. 1, a bypass capacitor 20 is shown electrically connected between an electrically conductive via 22 that is electrically connected to the power plane 12 and an electrically conductive via 24 that is electrically connected to the ground plane 14.
The purpose of the bypass capacitor 20 is to short together, at high frequencies, the power plane 12 and the ground plane 14, thereby filtering out any high frequency noise. However, because of parasitic inductance, capacitance, and resistance associated with the vies 22 and 24, the shorting capability, and thus the filtering capability, of the bypass capacitor 20 at high frequencies is diminished. Also, via inductance is more prevalent at high frequencies because the primary effect of series via inductance is that it degrades the effectiveness of power supply bypass capacitors, which defeats the whole power filtering strategy described above.
Attempts to solve the above-mentioned filtering problems have been pursued. For example, microvias have been used to shorten the length of vias, but they cannot eliminate vias completely. Also, via diameters have been reduced, thereby reducing the overall surface area over which parasitic inductance, capacitance, and resistance occur. However, changing the via diameter does little to influence via inductance. Thus, there remains a need for changing or eliminating the length of vias so as to improve power filtering performance.
In view of the foregoing, it would be desirable to provide a technique for improving power and ground filtering performance by changing or eliminating the length of electrically conductive vias which overcomes the above-described inadequacies and shortcomings.